As described in the above-discussed U.S. Pat. No. 3,804,282, a wide variety of products are now packaged in hermetically sealed plastic containers. The patent discloses a construction for a sealed plastic container that facilitates the opening of the container. The container includes a threaded cap and both the container and the cap (when screwed onto the container) appear visually to be generally conventional in all respects. By manipulating the cap, however, the user can cause the cap and container to coact and thereby open the container by severing a top or cover portion of the container from the remaining body portion at a weakened frangible web connection.
Operation of such a prior construction is briefly as follows. At the point of manufacture, the container is filled with the product, hermetically sealed, and the cap threaded onto the container neck or cover in the usual manner. To open the container, the user threadedly manipulates the cap to screw it further down onto the container. This causes an annular shoulder of the cap to bear against a mating annular shoulder on the container body portion to sever the cover.
While the described prior construction represented a notable advancement of the art, it was found that the force required to manipulate the cap and open the container sometimes became annoyingly excessive. The inventors of the present invention have determined that such increased required manipulating force resulted, to a large extent, from the relatively high frictional engagement between the coacting annular shoulders over their entire planar surface areas of contact. The degree of frictional resistance was related to, among other things, the annular shoulder areas and the coefficient of friction of the plastic materials employed.
Accordingly, the inventors of the present invention determined that it would be desirable to provide an improved plastic container and cap construction in which the frictional resistance between cap and container during the opening manipulation is greatly reduced.
Further, it would be beneficial to provide a container and cap construction of the character described which is adapted to be readily opened without the need of any additional implements.
It would also be advantageous to provide a container and cap construction of the character described which is simple in construction and operation and yet is inexpensive.
U.S. Pat. No. 4,051,972 shows a container cap having an undulating bottom edge. However, that cap is designed for use with glass containers or "Mason Jars" and the purpose of the undulating edge is to facilitate the passage of gases out of the jar during heating and preserving. There is no teaching that such a construction can be used with a severable container and in the manner of the present invention.